The present invention relates to a polyamide resin composition comprising a polyamide and an apatite type compound, having high strength and rigidity and is excellent in toughness so as to be suitably used as industrial materials for various mechanical parts and electrical/electronic parts, etc. and further being reduced in water absorption and warpage and excellent in rigidity upon water absorption, heat resistance, creep resistance, dimensional stability and moldability. The present invention also relates to a preparation process of the polyamide resin composition.
In order to improve the strength or rigidity which a polyamide resin originally has, it has been a common practice to incorporate, into a polyamide resin, various fillers including, for example, inorganic fibers such as glass fibers or carbon fibers, inorganic compounds such as calcium carbonate, mica or talc, or layered compounds such as montmorillonite and swelling fluorine mica. Although being effective for improving the strength or rigidity of the molded product of the resulting resin composition, these means are accompanied with the drawback that toughness which is another characteristic of the polyamide resin is markedly impaired owing to low affinity of the polyamide with a filler. JP-A-3-217454 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent application), discloses a polyamide resin composition comprising 100 parts by weight of a polyamide and 5 to 300 parts by weight of apatite aiming at obtaining a material having a touch feeling close to ivory. This composition is improved in strength and rigidity of the resulting molded product similar to the above-described compositions having a filler added thereto, but markedly low affinity at the interface between the polyamide and apatite causes a drastic decrease in toughness, that is, decrease in tensile elongation, which makes it difficult to use it as an industrial material.
Thus, reinforcement of a polyamide resin with various inorganic fillers has been proposed for the purpose of improving the strength and rigidity of a polyamide resin. Conventional proposals are however not fully satisfactory, because they cause a marked decrease in toughness, that is, tensile elongation, which imposes a limitation on the application of the polyamide resins. Accordingly, there is a demand for the development of a polyamide resin composition which has improved rigidity and strength without causing decrease in toughness.
An object of the present invention is to provide a polyamide resin composition which can overcome the above-described problems which have so far remained unsolved, in other words, a composition which has high strength and rigidity, while having excellent toughness, and moreover, which is reduced in water absorption and warpage and excellent in rigidity upon water absorption, heat resistance, creep resistance, dimensional stability and moldability.
To solve the above-described problems, the present inventors carried out an extensive investigation. As a result, it has been found that the above-described object can be accomplished by a specific polyamide composition obtained by incorporating a predetermined amount of an apatite type compound into a polyamide. Thus, the present invention has been completed.
That is, the present invention related to the following polyamide compositions (1) to (9) and preparation processes (10) to (18) therefor.
(1) A polyamide resin composition which contains 0.5 to 50 wt. % of an apatite type compound and which, when eluted with a phenol solvent and filtered, leaves 1 to 100 parts by weight of residual organic substances per 100 parts by weight of said apatite type compound.
(2) The polyamide resin composition according to the above item (1), wherein said polyamide has a weight-average molecular weight of 10,000 to 1,000,000.
(3) The polyamide resin composition according to the above item (1), wherein said organic substances comprise at least a polyamide.
(4) The polyamide resin composition according to the above item (1), wherein said apatite type compound has an average particle size not greater than 1 xcexcm.
(5) The polyamide resin composition according to the above item (1), wherein the molar ratio of the metal element(s) to phosphorus, both constituting the apatite type compound, is from 0.9 to 10.0.
(6) The polyamide resin composition according to any one of the above items (1) to (5), wherein said apatite type compound is a crystalline apatite compound which has a (002) plane peak at a diffraction angle (2xcex8) of 25.5xc2x0 to 26.5xc2x0 and a (300) plane peak at a diffraction angle (2xcex8) of 32.5xc2x0 to 33.5xc2x0 as observed by wide-angle X-rays (CuKxcex1: wavelength xcex=1.542 xc3x85) scattering.
(7) The polyamide resin composition according to any one of the above items (1) to (5), wherein said apatite type compound is represented by the following formula:
A10-z(HPO4)z(PO4)6-z(X)2-z.nH2O
wherein 0xe2x89xa6z less than 2, 0xe2x89xa6nxe2x89xa616, A represents a metal element and X represents an anion or an anionic compound.
(8) The polyamide resin composition according to the above item (5), wherein the metal element is at least one metal in Group 2A of the periodic table.
(9) The polyamide resin composition according to the above item (5), wherein the metal element is calcium.
(10) A process for preparing a polyamide resin composition, which comprises mixing a polyamide-forming component with an apatite type compound-forming component, allowing to proceed polymerization of a polyamide and synthesis of an apatite type compound, to give a composition in which an apatite type compound having an average particle size not greater than 1 xcexcm is dispersed in a polyamide having a weight-average molecular weight of 10,000 to 1,000,000.
(11) The process for preparing a polyamide composition according to the above item (10), wherein said polyamide-forming component comprises at least one selected from the group consisting of polymerizable amino acids, polymerizable lactams, and polymerizable salts of diamines and dicarboxylic acids, and polymerizable oligomers of these compounds.
(12) The process for preparing a polyamide resin composition according to the above item (10), wherein said apatite type compound-forming component comprises a phosphoric acid-based metal compound or a mixture of a phosphoric acid-based metal compound and a non-phosphoric acid-based metal compound.
(13) The process for preparing a polyamide resin composition according to the above item (10), wherein the molar ratio of the metal element(s) to phosphorus in said apatite type compound-forming component is from 0.9 to 10.
(14) The process for preparing a polyamide resin composition according to the above item (10), wherein said apatite type compound is a crystalline apatite compound having a (002) plane peak at a diffraction angle (2xcex8) of 25.5xc2x0 to 26.5xc2x0 and a (300) plane peak at a diffraction angle (2xcex8) of 32.5xc2x0 to 33.5xc2x0 as observed by wide-angle X-ray (CuKxcex1: wavelength xcex=1.542 xc3x85) scattering.
(15) The process for preparing a polyamide resin composition according to the above item (10), wherein said apatite type compound is represented by the following formula:
A10-z(HPO4)z(PO4)6-z(X)2-z.nH2O
wherein 0xe2x89xa6z less than 2, 0xe2x89xa6nxe2x89xa616, a represents a metal element and X represents an anion or an anionic compound.
(16) The process for preparing a polyamide resin composition according to the above item (12) or (13), wherein the metal element is at least one metal in Group 2A of the periodic table.
(17) The process for preparing a polyamide resin composition according to the above item (12) or (13), wherein the metal element is calcium.
(18) The process for preparing a polyamide resin composition according to the above item (10), wherein said polymerization of the polyamide and said synthesis of the apatite-type compound are carried out at a temperature of 40xc2x0 C. to 300xc2x0 C.